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Advanced Technologies for Networking in Avionic Applications

Final Report Summary - ATENAA (Advanced Technologies for Networking in Avionic Applications)

Future applications for CNS/ATM, AOC and cabin services require significant enhancements in aeronautical communications; digital links will be the cornerstone of next generation systems aiming to increase safety, capacity, efficiency and comfort in civil aviation.

Within such context, the ATENAA project has focused on the possible role of civilian aircraft as nodes of an ad-hoc network, capable of multi-hop transmission over omnidirectional and broadband directional data links. The key technological components investigated were:
- aeronautical mobile ad-hoc network protocols;
- Ka-band phased array antennas;
- free-space optics for inter-aircraft communications;
- free-space optics for inside-cabin data distribution.

The project objectives can be summarised as follows:
-Obj. 1: identification of areas of application for mobile ad-hoc networks in aeronautics;
-Obj. 2: identification of MANET routing protocols suitable for aeronautical applications and relative assessment via simulations;
-Obj. 3: methodologies and technologies to establish and maintain free space optics communication links between two platforms in relative motion, with identification of achievable performances;
-Obj. 4: low profile and price competitive airborne Ka-band phased-array antenna design with steering capability, by adoption of promising technologies;
-Obj. 5: feasibility study for a cabin free space optic system, which can deliver through diffused IR light, broadband communication to passengers;
-Obj. 6: reduced scale validation platforms for testing the different technologies and assessing their capabilities;
-Obj. 7: preparing a robust knowledge layer for subsequent related projects (e.g. MINERVAA).

The project performed research work in the following areas:
- define the concept for a future networked avionic environment including both moving platforms (aircraft and satellites), ground infrastructures and the related users and communication systems;
- evaluate and develop the technologies needed for the networking and the security of the avionic network;
- assess a common set of requirements for the advanced technologies under investigation;
- identify mobile ad-hoc network routing protocols suitable for aeronautical applications;
- assess HW technologies for Ka-band communication systems (with particular reference to TX and RX avionic phased array antenna realisation);
- assess HW technologies for optical communication systems for outside- aircraft data links realisation;
- assess HW technologies for optical communication systems for inside- aircraft broadband bus implementation;
- test and validate such emerging technologies against their applicability in the realisation of broadband communication systems for the avionic networked environment;
- dissemination of project results to a wider audience fostering the dialog with the research community and standardisation/normative bodies, through journal publications, conferences, organisation of a workshop and a constant updating of the project web page.

Developing and refining the concept of a unified future networked avionic environment including moving platforms (aircraft, high altitude platforms and satellites), ground infrastructures and the related users and communication systems was the initial step in defining the MANET network. This allowed an assessment of a common set of requirements for the various platforms and allowed to evaluate the capabilities of each of them and their possible role in the network. This in turn was a stepping-stone for the identification of the advanced protocol and data link technologies that would be required to realise the aeronautical MANET. The evaluation of existing MANET protocol technologies needed for the networking of the avionic network has been the next step. The literature review and subsequent comparison with the defined requirements led to identification of several gaps, which required the inclusion of additional functionality.

In particular the ATENAA protocol stack includes a Data Link Selection sub-layer, which allows to logically separating the network layer from the different data-links layers installed onboard. a custom-tailored routing protocol (GeODV) has been designed, which combines the advantages of MANET reactive and proactive protocols, and takes advantage of the aircraft geographical position information expected to be exchanged among aeronautical nodes.

The developed protocols have been modelled into the OPNET network simulator and the simulation results have been used to provide proof of concept for proposed protocols. Additional work was aimed at providing security extension to the above-mentioned routing protocol. Initially the ATN security mechanism was analysed and it's suitability to the MANET environment was determined. This was done in conjunction with an overview of MANET-specific security requirements. Then a comprehensive review of MANET secure routing and distributed key exchange algorithms was made to determine if and which protocols are suitable for use in the ATENAA network. Appropriate protocols were selected and integrated into the GeODV. Finally the performance of these protocols was briefly investigated theoretically.

Detailed link-budget calculations have been carried out considering free-space loss, atmospheric attenuation, receive telescope aperture, turbulence induced fading loss, receiver sensitivity, beam splitting for PAT and data receiver, miss-pointing, tracking errors, and further losses.

Main technology aspects used for free-space optical communication terminal design have been considered and analyzed, in particular with respect to modulation scheme, receive aperture size and beam divergence angle, system wavelengths, PAT-architectures, distances, IRT over link path, reliability and robustness as well as requirements from the network.

Basic concepts for FSO communication terminals have been analysed considering the peculiar application environment, discussing and evaluating several design trade-offs for terminal design. Communication and beacon channel wavelengths and critical electro/optical components have been evaluated and proposed. Stabilisation and tracking accuracies, together with pointing and acquisition time achievable figures have been provided considering affordable technologies in civil aeronautical environment.

A technological ground Validation Platform has been developed to allow concept and technology evaluation, in particular for what concerns acquisition time characteristics, communication robustness against obscurations, tracking and stabilisation performances.

Measurements of multipath limits have been carried out with the help of University of Oxford which has developed equipment to measure multipath behaviour. This method was applied in the cabin mock-up to achieve results from realistic environment. Hardware for modems and optical terminals has been developed. Validation of technological basis has been done by testing modems and terminals in a realistic environment (cabin mock-up), as realistic geometrical relations are very important for the investigated diffuse links. Principle tests have been carried out in lab environment, all final tests in the cabin mock-up.

The ATENAA project major findings can be summarised as follows:
- aeronautical mobile ad-hoc network protocols, despite the expected benefit which could provide to enhance capacity, flexibility and availability of current communications network, are still at an early maturity level;
- these protocols could find earlier application when utilised in conjunction with next generation VDL-like a/a data links (2020+), for providing low data rate services (ATS/AOC) to aircrafts in remote, polar, oceanic regions;
- aeronautical MANET networks utilising directional data links, could find earlier application in specific scenarios such as oceanic corridors;
- for wider application scenarios it is required substantial R&D activities before demonstrating feasibility of implementations and expected benefits;
- free space optics show that relatively stable Pt-To-Pt connections are possible with current technology;
- optical links among mobile platforms over 200..400 km / >100 Mbit/s are feasible with relatively compact terminals, if adopting proposed advanced fading mitigation techniques;
- wireless cabin optical links feasibility has been demonstrated, and could find short term applications both for passenger services and cabin crew communications;
- future activities on IOL should include wireless cabin optical technology integration into real applications, and on miniaturisation of optical terminals;
- targeted Ka-Band-a/c satellite links (Down 16 Mb/s ; Up 1 Mb/s) are achievable by use of -Low profile 1D steering patch array antenna concept which offers a cost effective solution;
- the flat 2D steering patch array antenna technology concept maturity has been increased and may allow enhancing system flexibility at a longer term.

The technology base developed within ATENAA has strong impact on further research (MINERVAA). Therefore the European industry started to fill the gap with respect to the US industry for what concerns FSO communication links for aeronautical mobile platforms. The capability of Ka-band phased array technology to ensure the expected data rate for satellite communications has been proven and solicited big interest of ADG members. The potential of the inner optical link was clearly demonstrated and strong interests have been fed back by the advisory group. The technology developed within ATENAA has shown strong impact on further research and is a large step towards short-midterm application in next generation aircraft cabins.